1. Field of the Invention
The present invention relates to a BLDC (Brushless Direct Current) motor, in particular to a method for detecting position of the BLDC motor which is capable of detecting position of a rotor of the BLDC motor when a phase voltage outputted from the BLDC motor is xe2x80x9c0xe2x80x9d.
2. Description of the Prior Art
FIG. 1 is a block diagram illustrating a construction of an apparatus for detecting position of a BLDC (Brushless Direct Current) motor according to the conventional technology. As depicted in FIG. 1, the apparatus comprises a position detecting pulse generation unit 11 outputting a position detecting pulse by being inputted a phase voltage generated when the BLDC motor operates and comparing it with a reference potential set in advance, a micro computer 12 controlling the BLDC motor in accordance with a position signal after recognizing an output of the position detecting pulse generation unit 11 as the position signal, its operation will now be described in detail with reference to FIG. 2.
FIGS. 2A through 2C are wave form diagrams illustrating wave forms of the each output signal in FIG. 1.
First, the BLDC motor controlled by a PWM (Pulse Width Modulation) signal generates a back electromotive force while operating. Herein, the phase voltage is equal to the back electromotive force of the BLDC motor 10 when the PWM signal applied to the BLDC motor 10 is in the ON state, the phase voltage is xe2x80x9c0xe2x80x9d when the PWM signal is in the OFF state and the phase voltage is generated as three phases and are separately inputted to the position detecting pulse generation unit 11. The position detecting pulse generation unit 11 outputs the position detecting pulse by using the inputted three phases (Ref. FIG. 2A).
The position detecting pulse generation unit 11 outputs the position detecting pulse to the micro computer 12 which is a xe2x80x9chigh potentialxe2x80x9d when the phase voltage is bigger than a reference potential Vf, or is a xe2x80x9clow potentialxe2x80x9d when the phase voltage is smaller than the reference potential Vf.
After that, the micro computer 12 detects a time point when the position detecting pulse is became the xe2x80x9chigh potentialxe2x80x9d initially by an interrupt signal, determines the time point as a position detecting time point of the BLDC motor 10, and operates the BLDC motor by controlling a driving unit (not shown) in accordance with the position detecting time point.
However, as depicted in FIG. 2C, in the apparatus for detecting position of the BLDC motor according to the conventional technology, when the phase voltage outputted from the motor is xe2x80x9c0xe2x80x9d, the position detecting pulse generation unit 11 can not detecting the time point when the back electromotive force is bigger than the reference potential, accordingly a position detecting error xcex94t occurs.
The object of the present invention is to provide a method for detecting position of a BLDC (Brushless Direct Current) motor which is capable of detecting accurately a crossing time point of a back electromotive force and a reference potential by using a phase voltage outputted from the BLDC motor regardless of ON/OFF operation of a PWM (Pulse Width Modulation) signal inputted to the BLDC motor.
In order to achieve the object, the method of the present invention comprises a storing step storing the phase voltage outputted from the motor as a previous phase voltage with a detecting time detecting it when the phase voltage outputted from the motor is smaller than a reference potential set in advance, and a determining step determining a position detecting time point by using the stored detecting time after storing the phase voltage outputted from the motor as the present voltage when the phase voltage outputted from the motor is bigger than the reference potential set in advance.